U.S. patent number 7,536,154 [Application Number 10/726,374] was granted by the patent office on 2009-05-19 for reliability detection of channel quality indicator (cqi) and application to outer loop power control.
This patent grant is currently assigned to InterDigital Technology Corporation. Invention is credited to Stephen G. Dick, James M. Miller, Marian Rudolf.
United States Patent |
7,536,154 |
Rudolf , et al. |
May 19, 2009 |
**Please see images for:
( Certificate of Correction ) ** |
Reliability detection of channel quality indicator (CQI) and
application to outer loop power control
Abstract
A method for improving the reliability of a channel quality
indicator (CQI) message in a wireless communications network begins
with receipt of the CQI message. The CQI message is then decoded,
and a decision metric value for each symbol in the CQI message is
computed. A largest decision metric value and a second largest
decision metric value for the CQI message are determined. The
reliability of the CQI message can be determined by comparing the
two largest decision metric values. This method may be applicable
to high-speed downlink packet access in time division duplex,
frequency division duplex, or other modes of transmission.
Inventors: |
Rudolf; Marian (Montreal,
CA), Dick; Stephen G. (Nesconset, NY), Miller;
James M. (Verona, NJ) |
Assignee: |
InterDigital Technology
Corporation (Wilmington, DE)
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Family
ID: |
32474599 |
Appl.
No.: |
10/726,374 |
Filed: |
December 3, 2003 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20040110473 A1 |
Jun 10, 2004 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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60430854 |
Dec 4, 2002 |
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60438560 |
Jan 6, 2003 |
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Current U.S.
Class: |
455/69;
455/67.13; 455/452.2; 455/135; 370/342; 370/335 |
Current CPC
Class: |
H04L
1/20 (20130101); H04L 43/16 (20130101); H04W
52/12 (20130101); H04L 1/0033 (20130101); H04W
52/262 (20130101); H04W 52/20 (20130101); H04L
1/0026 (20130101); H04L 5/006 (20130101); H04W
48/08 (20130101); H04W 72/0413 (20130101); H04W
52/0225 (20130101); Y02D 30/70 (20200801); H04L
1/0003 (20130101); H04L 2001/125 (20130101); H04L
1/1671 (20130101); H04W 28/24 (20130101) |
Current International
Class: |
H04B
7/00 (20060101) |
Field of
Search: |
;455/69,562.1,561
;370/335,342,328,329 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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95/21494 |
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Aug 1995 |
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WO |
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03/019820 |
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Mar 2003 |
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WO |
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03/073644 |
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Sep 2003 |
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WO |
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Other References
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.
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Group Radio Access Network; Physical Layer Procedures (FDD)
(Release 5)." 3GPP TS 25.214 v5.2.0 (Sep. 2002). cited by other
.
3GPP, "3.sup.rd Generation Partnership Project; Technical Support
Group Radio Access Network; Physical Layer Procedures (FDD)
(Release 5)." 3GPP TS 25.214 v5.6.0 (Sep. 2003). cited by other
.
3GPP, "3.sup.rd Generation Partnership Project; Technical Support
Group Radio Access Network; Physical Channels and Mapping of
Transport Channels onto Physical Channels (FDD) (Release 1999),"
3GPP TS 25.211 V3.12.0 (Sep. 2002). cited by other .
3GPP, "3.sup.rd Generation Partnership Project; Technical Support
Group Radio Access Network; Physical Channels and Mapping of
Transport Channels onto Physical Channels (FDD) (Release 4)," 3GPP
TS 25.211 V4.6.0 (Sep. 2002). cited by other .
3GPP, "3.sup.rd Generation Partnership Project; Technical Support
Group Radio Access Network; Physical Channels and Mapping of
Transport Channels onto Physical Channels (FDD) (Release 5)," 3GPP
TS 25.211 V5.2.0 (Sep. 2002). cited by other .
3GPP, "3.sup.rd Generation Partnership Project; Technical Support
Group Radio Access Network; Physical Channels and Mapping of
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TS 25.211 V5.5.0 (Sep. 2003). cited by other .
3GPP, "3.sup.rd Generation Partnership Project; Technical Support
Group Radio Access Network; High Speed Downlink Packet Access
(HSDPA); Overall Description; Stage 2 (Release 5)," 3GPP TS 25.308
V5.2.0 (Mar. 2002). cited by other .
3GPP, "3.sup.rd Generation Partnership Project; Technical Support
Group Radio Access Network; High Speed Downlink Packet Access
(HSDPA); Overall Description; Stage 2 (Release 5)," 3GPP TS 25.308
V5.4.0 (Mar. 2003). cited by other .
3GPP, "3.sup.rd Generation Partnership Project; Technical Support
Group Radio Access Network, MAC Protocol Specification (Release
1999)," 3GPP TS 25.321 v3.13.0 (Sep. 2002). cited by other .
3GPP, "3.sup.rd Generation Partnership Project; Technical Support
Group Radio Access Network; Medium Access Control (MAC) Protocol
Specification (Release 1999)," 3GPP TS 25.321 v3.16.0 (Sep. 2003).
cited by other .
3GPP, "3.sup.rd Generation Partnership Project; Technical Support
Group Radio Access Network; MAC Protocol Specification (Release
4)," 3GPP TS 25.321 v4.6.0 (Sep. 2002). cited by other .
3GPP, "3.sup.rd Generation Partnership Project; Technical Support
Group Radio Access Network; Medium Access Control (MAC) Protocol
Specification (Release 4)," 3GPP TS 25.321 v4.9.0 (Sep. 2003).
cited by other .
3GPP, "3.sup.rd Generation Partnership Project; Technical Support
Group Radio Access Network; Physical Layer Procedures (FDD)
(Release 1999)," 3GPP TS 25.214 v3.11.0 (Sep. 2002). cited by other
.
3GPP, "3.sup.rd Generation Partnership Project; Technical Support
Group Radio Access Network, MAC Protocol Specification (Release
5)," 3GPP TS 25.321 v5.2.0 (Sep. 2002). cited by other .
3GPP, "3.sup.rd Generation Partnership Project; Technical Support
Group Radio Access Network; Medium Access Control (MAC) Protocol
Specification (Release 5)," 3GPP TS 25.321 v5.6.0 (Sep. 2003).
cited by other .
3GPP, "3.sup.rd Generation Partnership Project; Technical Support
Group Radio Access Network; Physical Layer Procedures (FDD)
(Release 1999)," 3GPP TS 25.214 v3.12.0 (Mar. 2003). cited by other
.
3GPP, "3.sup.rd Generation Partnership Project; Technical Support
Group Radio Access Network; Physical Layer Procedures (FDD)
(Release 4)," 3GPP TS 25.214 v4.5.0 (Sep. 2002). cited by
other.
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Primary Examiner: Anderson; Matthew D
Assistant Examiner: Dao; Minh D
Attorney, Agent or Firm: Volpe and Koenig, P.C.
Claims
What is claimed is:
1. A method for determining a channel quality in a wireless
communication system, comprising: receiving a high speed shared
control channel (HS-SICH) transmission; counting a total number of
HS-SICH transmissions; counting a number of failed HS-SICH
transmissions; counting a number of missed HS-SICH transmissions;
and periodically reporting the total number of HS-SICH
transmissions, the number of failed HS-SICH transmissions, and the
number of missed HS-SICH transmissions over a fixed time period,
whereby the reporting is an indication of the channel quality.
2. A base station configured to determine a channel quality,
comprising: a receiver configured to receive a high speed shared
control channel (HS-SICH) transmission; a counter configured to
count a total number of HS-SICH transmissions, a number of failed
HS-SICH transmissions, and a number of missed HS-SICH
transmissions; and a reporting device configured to periodically
report the total number of HS-SICH transmissions, the number of
failed HS-SICH transmissions, and the number of missed HS-SICH
transmissions over a fixed time period, whereby the report is an
indication of the channel quality.
3. A base station configured to determine a channel quality,
comprising: a receiver configured to receive a high speed shared
control channel (HS-SICH) transmission; a first counter configured
to count a total number of HS-SICH transmissions; a second counter
configured to count a number of failed HS-SICH transmissions; a
third counter configured to count a number of missed HS-SICH
transmissions; and a reporting device configured to periodically
report the values of said first counter, said second counter, and
said third counter over a fixed time period, whereby the report is
an indication of the channel quality.
4. A wireless transmit/receive unit (WTRU), comprising: a
transmitter configured to transmit a plurality of high speed shared
control channel (HS-SICH) transmissions; a receiver configured to
receive a power control command, the power control command being
derived by counting a total number of HS-SICH transmissions,
counting a number of failed HS-SICH transmissions, counting a
number of missed HS-SICH transmissions, and comparing the counted
values to a predetermined threshold; and a transmission power
adjusting device configured to adjust an uplink transmission power
of the WTRU based on the power control command.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims priority from U.S. patent application Ser.
No. 60/430,854, filed on Dec. 4, 2002, and from U.S. patent
application Ser. No. 60/438,560, filed on Jan. 6, 2003, which are
incorporated by reference as if fully set forth herein.
FIELD OF INVENTION
The present invention relates generally to channel quality
measurements in wireless communications, and more particularly, to
a method and apparatus for reliably detecting channel quality and
its application to outer power loop control.
BACKGROUND
Currently, third generation (3G) mobile communication systems are
being standardized to implement efficient and high throughput of
downlink (DL) packet data transfer mechanisms. In the context of
universal mobile telecommunications system (UMTS) wideband
code-division multiple access (W-CDMA) based 3G systems, these
packet transfer techniques are commonly referred to as high-speed
downlink packet access (HSDPA). HSDPA is possible for both
Frequency Division Duplex (FDD) and Time Division Duplex (TDD)
modes, and is implemented for chip rates of 1.28 Mcps and 3.84
Mcps.
The following characteristic features are the source of recognized
efficiency and achievable data throughput of HSDPA: Adaptive
Modulation and Coding (AMC) techniques; fast Hybrid Automatic
Repeat Request (Hybrid ARQ); fast feedback mechanism for uplink
(UL) reporting of instantaneous DL channel quality; and radio
resource efficient packet scheduling mechanism and fast, short-term
DL channel assignments.
Yet another distinguishing feature of HSDPA is that the data rate
and amount of DL transmission (Tx) power that an HSDPA base station
allocates to a wireless transmit and receive unit (WTRU) is a
function of the WTRU's instantaneous channel conditions. For
example, a user close to the base station can reliably receive a
high HSDPA data rate with low transmission power. A user far away
from the base station, or a user confronted with unfavorable
channel conditions, would only support a reduced data rate for the
same or higher amount of allocated DL transmission power.
The instantaneous HSDPA data rate that a particular user can
reliably support is generally dependent on: 1) path loss, which is
based on the distance to the serving base station; 2) shadowing; 3)
instantaneous fast fading conditions; 4) interference at the user's
receiver caused by other users present in the system; and 5) the
user's channel conditions, such as the speed and propagation
environment. In other words, the HSDPA data rate is a function of
the user's experienced DL signal-to-interference ratio (SIR) which
is based upon all of these factors and is representative of the DL
data rate that the user can support. The user's DL SIR will
generally vary in time as a function of these factors.
Knowledge of the user's experienced DL SIR or any similar
representative metric with this functionality, for example BLER,
BER, or received signal power combined with received DL
interference, is essential for the HSDPA base station to ensure
highly efficient HSDPA operation. CDMA systems employing HSDPA have
therefore adopted a fast UL Layer 1 (L1) signaling mechanism which
allows a WTRU to periodically report the DL SIR to the base station
with a fast, UL channel quality indicator (CQI). The current FDD
specification allows configuration of the periodic CQI feedback in
the UL to be sent every 0 (when CQI reporting is turned off), 2, 4,
8, 10, 20, 40, 80, or 160 ms. However, in TDD there is no periodic
CQI feedback, so the CQI is instead sent with an ACK/NACK on the
High-Speed Shared Control Channel (HS-SICH) whenever a DL data
block on the HSDPA Data Channel (HS-DSCH) is received by a WTRU. In
W-CDMA FDD and TDD modes, this mechanism is commonly referred to as
CQI reporting.
The method for measuring a CQI in a particular WTRU implementation
is not standardized, but is open to vendor implementation. But the
method of how to derive the reported CQI value is standardized. In
the FDD standard, there is a table (as shown in 3GPP TS 25.321,
Medium Access Control (MAC) Protocol Specification, 5.4.0
(2003-03)) listing some 30 CQI values roughly corresponding to
increasingly higher data rates, and therefore proportional to
higher and higher DL SIRs. The reported CQI in FDD is derived as
follows (per 3GPP TS 25.214, Physical layer procedures (FDD),
v5.4.0 (2003-03), section 6A.2): "the UE shall report the highest
tabulated CQI value for which a single HS-DSCH sub-frame formatted
with the transport block size, number of HS-PDSCH codes and
modulation corresponding to the reported or lower CQI value could
be received in a 3-slot reference period ending 1 slot before the
start of the first slot in which the reported CQI value is
transmitted and for which the transport block error probability
would not exceed 0.1." In TDD, the reporting is different; the
transport block size is reported if it was transmitted during the
last received transmission interval (the number of timeslots where
the last HS-DSCH was received) and that transmission would have
yielded a block error rate of 0.1.
As an example, in the current W-CDMA FDD release 5, the CQI is an
information bit sequence five bits long which is encoded by means
of a (20, 5) Reed-Muller code. The resulting 20 bit long coded
sequence is sent in the UL on a High-Speed Dedicated Physical
Control Channel (HS-DPCCH). Every user has a separate HS-DPCCH with
an adjustable CQI reporting cycle (feedback rate). A user can
report the CQI on the HS-DPCCH even if the user does not receive
data on the HS-DSCH.
As another example, in the current W-CDMA TDD release (3.84 Mcps or
high chip rate (HCR) TDD), the CQI is an information bit sequence
ten bits long which is encoded by means of a (32, 10) Reed-Muller
code. The resulting 32 bit long coded sequence is sent in the UL as
part of the HS-SICH. With current TDD, a CQI transmission can only
take place if the user has previously received data on the HS-DSCH
in the frame.
Because the reliability of a WTRU's CQI report has an impact on
HSDPA operation, it is important that an HSDPA base station has a
means of determining whether a CQI was received in error. By
discarding any erroneously received CQI, the HSDPA base station can
avoid the situation in which it would choose a DL data rate and
corresponding transmission power for a user that is not adapted to
the user's experienced DL channel conditions. Erroneous CQIs reduce
the HSDPA data throughput to the user and create a high level of
interference to the other users in the system, which reduces the
efficiency of HSDPA service in the W-CDMA system.
Furthermore, too many CQIs received in error from a particular user
are an indication that the user's UL transmission power settings
are not accurate and the base station or another access network
node, such as the Radio Network Controller (RNC), will take
appropriate actions. As an example, the RNC can signal a higher
target UL SIR to the user in order to increase its UL transmission
power and to lower the error rate on HS-DPCCH (in FDD) or HS-SICH
(in TDD). This type of RNC functionality is commonly referred to as
outer loop power control.
Error detection of received UL transmissions in W-CDMA FDD and TDD
modes is typically accomplished by employing a Cyclic Redundancy
Check (CRC), i.e., a bit sequence computed from and accompanying
the data which, when decoded in error in the base station, is a
reliable indicator of decoding errors. For a CRC to be effective in
error detection, the length of the CRC must be sufficiently large.
However, in order to avoid having an inefficient process, the ratio
of the CRC length to the actual data length must be small. In a
typical application, the data may be on the order of hundreds of
bits while the CRC field may be on the order of 8-24 bits.
Unfortunately, the HS-DPCCH (FDD) and the HS-SICH (TDD) are fast L1
UL signaling channels which do not include any UL data or a
sufficient number of L1 signaling bits to make efficient use of a
CRC. To provide sufficient error detection capabilities, the CRC
would have to be nominally at least the same size as the data field
that it is verifying. With these considerations, current HSDPA
standards do not use a CRC on the HS-DPCCH (FDD) and the HS-SICH
(TDD).
Therefore, based on existing techniques the network (base station
or RNC) has no means of reliably determining whether or not a CQI
was received in error or not. The network can only configure the
WTRU to use a high enough UL transmission power by means of an UL
target SIR and by "experience" from simulations, such that the
event of errors is sufficiently unlikely and not detrimental to
HSDPA system operation. It is therefore advantageous to provide a
method for reliably detecting and reporting the correctness of
received CQI values.
SUMMARY
The method of the present invention enables the base station to
determine the degree of reliability of the CQI. The present
invention provides a useful reliability detection mechanism for a
CQI report received by the HSDPA base station from a WTRU and
provides a received CQI quality reporting mechanism from the HSDPA
base station to the RNC in order to track and adjust a WTRU's UL
transmitting power setting.
A method for improving the reliability of a channel quality
indicator (CQI) message in a wireless communications network begins
with receiving and decoding the CQI message. A decision metric
value for each symbol in the CQI message is computed. A largest
decision metric value and a second largest decision metric value
are determined. The reliability of the CQI message is determined by
comparing the largest decision metric value and the second largest
decision metric value.
A method for improving the reliability of a received message
representing quality of a transmission channel in a wireless
communication system begins by receiving a channel quality
indicator (CQI) message from a wireless transmit and receive unit.
The CQI message is then decoded, and at least two different values
representative of the decoded CQI message are obtained. The
reliability of the CQI message is determined by comparing the at
least two values.
A system for determining the quality of a transmission channel in a
wireless communication system includes at least one wireless
transmit and receive unit (WTRU) and a base station. The WTRU
includes generating means for generating a channel quality
indicator (CQI). The base station includes receiving means for
receiving the CQI, decoding means for decoding the CQI, computing
means for computing a first decision metric and a second decision
metric of the decoded CQI, and comparing means for comparing the
first and second decision metrics to determine if the CQI contains
an error.
An integrated circuit constructed in accordance with the present
invention includes an input configured to receive a channel quality
indicator (CQI) message, decoding means for decoding the CQI
message, computing means for computing a first decision metric and
a second decision metric of the decoded CQI message, and comparing
means for comparing the first and second decision metrics to
determine if the CQI message contains an error.
BRIEF DESCRIPTION OF THE DRAWINGS
A more detailed understanding of the invention may be had from the
following description of preferred embodiments, given by way of
example and to be understood with reference to the accompanying
drawings, in which:
FIG. 1 is a flowchart of a method in accordance with the present
invention, applicable to both FDD and TDD;
FIG. 2 is a flowchart of an alternate embodiment of a method in
accordance with the present invention, applicable to both FDD and
TDD;
FIG. 3 shows an example of CQI reliability detection, applicable to
both FDD and TDD;
FIG. 4 is a graph of the additive white Gaussian noise (AWGN)
channel HS-SICH performance, from TDD simulations; and
FIG. 5 is a graph of the WG4 test case 2 channel HS-SICH
performance, from TDD simulations.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
As used and described hereafter, a WTRU includes, but is not
limited to, a user equipment, a mobile station, a fixed or mobile
subscriber unit, a pager, or any other type of device capable of
operating in a wireless environment. When referred to hereafter, a
base station includes, but is not limited to, a Node-B, a site
controller, an access point, or other type of interfacing device in
a wireless environment.
FIG. 1 illustrates a method 100 for determining the reliability of
a CQI and its application to outer loop power control in accordance
with the present invention. The method 100 begins by initializing a
time interval clock and several counters, such as total HS-SICHs
received, number of false HS-SICHs received, and number of HS-SICHs
that have been missed (step 102). The CQI is received (step 104)
and decoded (step 106). For each symbol in the CQI, a decision
metric value is computed (step 108). The two largest decision
metric values are selected (step 110) and the difference between
the two largest values is determined (step 112). The difference
between the two largest decision metrics is evaluated to determine
if it is below a threshold (step 114). If the difference is below
the threshold, then the CQI is likely to be in error, so it is
discarded (step 116).
If the difference meets or exceeds the threshold, then the CQI is
presumed to be valid (step 118). Next, the counters are incremented
(step 120) and a determination is made whether the end of the time
interval has been reached (step 122). Also, flow passes back to
step 104; the loop of steps 104-120 repeats continuously,
regardless of the value of the counters or whether the time
interval has expired.
If the time interval has expired (step 122), then a determination
is made whether the counters meet or exceed a threshold value (step
124). If the counters are equal to or greater than the threshold,
the RNC is signaled (step 126), the RNC then signals the WTRU to
adjust the UL transmission power (step 128), and the method ends
(step 130). If the end of the time interval has not been reached
(step 122) or if the counters are below the threshold (step 124),
then the method ends (step 130).
It is noted that the difference determined in step 112 is
applicable when the metric are logarithmic, i.e., in dB. If the
metrics are in pure numbers, then steps 112 and 114 can be modified
as follows. The ratio of the largest decision metric to the second
largest decision metric is calculated (step 112) and the ratio is
compared to the threshold (step 114).
A similar alternate method involving additional Iub signaling
entails simple periodic reporting of the total number of HS-SICHs
received, the number of false HS-SICHs received, and the number of
HS-SICHs that have been missed over a fixed time period and
reporting these numbers without regard to error thresholds. This
type of periodic reporting would add more Iub signaling, but would
be less complex to implement in the Node B.
FIG. 2 shows an alternate method 200 for determining the
reliability of a CQI and its application to outer loop power
control in accordance with the present invention. The method 200
begins by initializing several counters, such as total HS-SICHs
received, number of false HS-SICHs received, and number of HS-SICHs
that have been missed (step 202). The CQI is received (step 204)
and decoded (step 206). For each symbol in the CQI, a decision
metric value is computed (step 208). The two largest decision
metric values are selected (step 210) and the difference between
the two largest values is determined (step 212). The difference
between the two largest decision metrics is evaluated to determine
if it is below a threshold (step 214). If the difference is below
the threshold, then the CQI is likely to be in error, so it is
discarded (step 216).
If the difference is above the threshold, then the CQI is presumed
to be valid (step 218). Next, the counters are incremented (step
220) and a determination is made whether the counters meet or
exceed a threshold value (step 222). Also, flow passes back to step
204; the loop of steps 204-220 repeats continuously, regardless of
the value of the counters.
If the counters are equal to or greater than the threshold, the RNC
is signaled (step 224), the RNC then signals the WTRU to adjust the
UL transmission power (step 226), and the method ends (step 228).
If the counters are below the threshold (step 222), then the method
ends (step 228).
When the base station decodes the received 32 bit code word (steps
106, 206), the output of the decoding process can be viewed as one
of N distinct hypotheses, where the number of information bits n is
related to M by M=2.sup.n (in TDD, n=10). In other words, one out
of M symbols is sent from the WTRU to base station. The hypothesis
test at the base station selects the most likely member of the M
symbol alphabet, and then converts it back into the n information
bits that the symbol, i.e., the encoded code word, represents.
Different decision algorithms exist to determine what represents
the most likely received symbol, often varying on what is known
about the symbols. For example, if it is more likely that a
particular symbol is sent, then incorporating this knowledge into
the decision algorithm provides an advantage over an algorithm
which supposes that all symbols are sent equally often. To further
illustrate, in the FDD context, the decoder can operate like 32
matched filters, with one filter for each symbol, wherein each
symbol has a particular waveform (chip/bit sequence). Each matched
filter correlates the received waveform with the waveform
corresponding to a particular symbol. The correlation outputs from
each of the 32 matched filters is basically a peak corresponding to
energy. A large peak means that "very likely this was the symbol
sent" (wherein a code word is equivalent to a chip sequence), and a
small correlation peak means that "unlikely this was the right
symbol." Then, the largest peak out of the 32 obtained peaks is
selected and is determined to be the symbol that was sent. Because
this is a statistical hypothesis test, on average the determined
symbol is the best decision that can be made. An example of this
process is shown in FIG. 3. The decoding process in the base
station converts a sequence of received channel bits into soft
decision metrics for every possible one out of M CQI symbols. The
CQI quality detector can be implemented in a single integrated
circuit or as discrete components.
In general, the information bit sequence (the CQI word) is n bits
long. The CQI word is encoded to a (N,n) Reed-Muller code, which
consists of M (=2^n) N-bit long encoded bit sequences. For example,
in TDD, there are n=10 information bits, which results in 1024
(M=2^10) possible encoded words of length N=32 bits each. The
process of encoding the CQI on the HS-SICH provides some
repetition, which maps each of the N coded bits into N*4=L channel
bits. Every channel bit is spread by a spreading factor of 16
(i.e., a 16 chip long spreading sequence), resulting in L*16=C
chips. In TDD, the CQI word is generally encoded using a (32,10)
Reed-Muller encoding and n=10, N=32, L=128, C=2048. Without loss of
generality, the same principle of the method is also valid for FDD
with a (16,5) encoding.
As those of skill in the art would realize, any other type of
encoding scheme may be used, and the present invention is not
limited to the schemes set forth herein. An arbitrary (N,n)
encoding scheme as known by channel coding theory and existing for
the choice of parameters n and N, determining its ratio of
information bits to coded channel bits would operate with the
present invention. For example, a Reed-Muller first or second order
code or a Reed-Solomon code could be used. The particular coding
scheme on the (N,n) bits is not significant, as long as the decoder
can compute discrete decision metrics for each and every symbol
that can be sent over the channel.
Steps 110 and 112 of FIG. 1 and steps 210 and 212 of FIG. 2
represent one possible method to determine CQI reliability.
Numerous other methods for determining CQI reliability are
possible. For example, the ratio of the greatest or largest
decision-metric to the second greatest, or the difference between
these two metrics in dB (10 log (ratio)) may be used. To illustrate
by way of some simple equations, if P.sub.max denotes the value of
the largest observed peak and P.sub.second denotes the
second-largest observed peak, the ratio (R) could be expressed as
R=P.sub.max/P.sub.second or log(P.sub.max)/log(P.sub.second) or
more generally as f(P.sub.max/P.sub.second). Another proposed
method of determining CQI reliability is the ratio of the energy of
the greatest decision metric to the sum or a weighted sum of the
energy of the set of M-1 other decision metrics. For example,
P.sub.i (i=1 . . . 32) are values of the observed peaks at the
output of the Reed-Muller decoder. P.sub.max is the maximum P.sub.i
value. The measure R is expressed as
R=P.sub.max/(.SIGMA.P.sub.i-P.sub.max).
By comparing the soft decision metrics of the decoded CQI symbols,
the base station can employ a simple threshold-based decision
mechanism in order to decide whether the received CQI symbol is
likely to be or not to be in error (steps 114, 214). As an example,
if the difference between greatest and second greatest metric is
less than 1 dB, there is a very high probability (typically,
greater than 95%) that the CQI is in error and the CQI should be
discarded. Other difference values may be used, with a
corresponding reduced probability of the CQI being in error. A
preferred range for the difference is between 0-2 dB, so that the
probability of the CQI being in error is sufficiently high.
An example of the CQI reliability detection method performance in
terms of the ability to detect CQI errors for the TDD case is shown
in FIGS. 4 and 5. FIGS. 4 and 5 include graphs for BER after MUD,
ACK->NACK BER, NACK->ACK BER, rejected CQIs, rejected CQIs
which were good, and not rejected CQIs which were false. The graphs
also include RMF BER, which is the first bit of the ten bit long
CQI word and indicates the Recommended Modulation Format (either
QPSK or QAM). The graphs show the BER for this single bit. The RTBS
includes the other nine information bits in the CQI word and they
denote the Recommended Transport Block Set, which is the number of
information bits in the HS-DSCH transport block that the WTRU
recommends should be sent. The graphs show the word error rate
(WER) of these nine bits, which indicates the probability that at
least one of the nine RTBS bits is in error.
The following observations may be made from FIGS. 4 and 5: 1) the
ACK/NACK soft decision threshold is at 0.1*signal amplitude; 2) the
criteria to reject a CQI includes the highest/second highest
correlation peaks less than 1 dB away in amplitude; 3) erroneous
CQIs can be readily detected; and 4) the ratio of "correct CQIs
falsely rejected" to "wrong CQIs not rejected" can be easily scaled
to meet target errors.
Thus, an improved CQI field coding is made possible by the use of
the present invention. Under previous methods, when the HS-SICH
carrying the ACK/NACK and the CQI was received, there was no means
of knowing if the received HS-SICH fields (either the ACK/NACK or
the CQI) were received in error, because there was no CRC. If the
ACK/NACK is received in error and the Node B does not realize this,
the Node B could, for example, retransmit a packet that was already
received successfully in the WTRU or discard (not retransmit) a
packet which it should have retransmitted and WTRU waits for an
extended period of time for a packet that will never arrive and
memory stalls. The CQI reliability detection according to the
present invention allows the Node B to indicate which received
HS-SICHs are reliable and can take appropriate actions, like
retransmission. Also, in order to ensure reasonably often (<1%
of the cases when received) that the HS-SICH is reliable, the
HS-SICH needs to be received at a high SNR. This means that the
WTRU must transmit at a higher power. Because the WTRU does not
have much power and to be able to maximize coverage, the WTRU's
transmission power must be sufficient to meet the average HS-SICH
BER of 0.1. The proposed CQI reliability detection methods provide
the Node B, via reporting the CQI, the means of tracking the
current transmission power settings in the WTRU and the means to
adjust the power settings.
Furthermore, the reliability detection method can also be used to
provide indicators to the HSDPA base station and the RNC on
HS-SICH/HS-DPCCH performance and CQI reporting, to alert the HSDPA
base station that the CQI value may be in error. It is also
possible to alert, through a message from the HSDPA base station to
the RNC via the Iub/Iur network interfaces, that the delivered SIR
may be inadequate. Simple statistics are provided, such as how many
received HS-SICHs received from a particular WTRU were declared in
error based on CQI metrics, how many total HS-SICHs were received
over the same time period, and how many HS-SICHs were declared not
to have been sent at all. These are functions that would normally
be provided by a CRC and which now are possible due to the CQI
reliability test based on soft decision metrics.
According to a particular aspect of the invention, new messages are
added to the Iub/Iur network interface to define occurrences of the
number of failures of a transmission and the number or occurrences
of symptom-free receptions, i.e., to report that a given WTRU has
sent X successive UL HS-SICH messages without a failure being
reported.
Upon reception of a predetermined number of CQI failure indicators
related to a particular WTRU or HS-SICH channel, either the HSDPA
base station or the RNC can take appropriate actions, such as
changing the power control parameters for the WTRU or the HS-SICH
channel, or discarding CQIs and using previous CQI reports for DL
HSDPA transmissions. In one embodiment of the present invention
(shown in FIG. 1), counts are taken over 200 ms time intervals. In
each frame (which is 10 ms long), there can be at most one HS-SICH
received from a WTRU, so therefore there are at most 20 HS-SICHs in
200 ms. All counters are defined from 0 . . . 20 (total received
HS-SICHs, false HS-SICHs, and missed HS-SICHs).
Even though the examples given above are directed to HSDPA TDD, the
invention is equally applicable to HSDPA FDD and other modes of
transmission, for obtaining improved CQI reliability detection and
improved outer loop power control. While specific embodiments of
the present invention have been shown and described, many
modifications and variations could be made by one skilled in the
art without departing from the scope of the invention. The above
description serves to illustrate and not limit the particular
invention in any way.
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